This invention relates generally to devices for isolating and containing gas reactive materials. Particularly, this invention relates to gas purifiers, filters and monitors that are useful in the microelectronics manufacturing industry. More particularly, this invention relates to gas purifiers having an in-gland diaphragm valve assembly for isolating and containing gas to be purified from the surrounding environment.
Devices of various types for purifying, filtering or monitoring gases are used widely in the industry. For example, gases used in the fabrication of semiconductors must be of ultrahigh purity as the semiconductor chip geometry has become smaller. Gas purifiers have been used in the microelectronics industry for many years to remove molecular and particulate contamination from these gases.
Since many of the gases used in semiconductor manufacturing are toxic or corrosive, they can pose environmental and health concerns if they become exposed to the surrounding environment. Gas purifiers are typically disposable devices since the reactive material used as the purifier element is consumed upon use. Additionally, upon installation the surrounding environment can enter the purifier thereby consuming a portion of its useful life. This exposure to the surrounding environment also lengthens the preparation time for the gas line as moisture and other impurities must be purged from the system prior to use. Consequently, there is a need to isolate the purifier from the gas supply line and to contain any gas within the purifier during installation and removal of the purifier. Most often this isolation and containment during changeout of the purifier is accomplished through the use of a pair of isolation valves positioned externally of the purifier element adjacent the inlet and outlet fittings which attach the purifier to the gas supply line. The primary function of the isolation valves is to enhance safety when removing the disposable purifier from the gas line during maintenance and to protect the reactive purifier material from exposure to the surrounding environment. However, the disadvantage of using external isolation valves is that they are expensive, increase the internal volume of the system and also add to the overall bulkiness of the purifier. Such bulkiness creates significant additional costs, especially since semiconductors are manufactured in a clean room environment.
Attempts have been made to eliminate the need for external valves in gas purifiers. An example of such a design is shown in U.S. Pat. No. 5,139,747 which discloses a gas purifier with poppet valves which are integrally located within the purifier element thereby eliminating the need for external valves. Because specially designed gaskets are used, a large force is required to actuate the poppet valves. Thus, this patent teaches using a pair of spring stacks, one at the inlet and the other at the outlet, to apply sufficient force on the poppet valve necessary to make a reliable seal. FIG. 1 is a cross-section of a poppet valve arrangement representative of the type used in U.S. Pat. No. 5,139,747. The use of springs is undesirable because they are a potential source of contamination due to their increased surface area, the majority of which is not swept by the fluid thereby producing significant dead volume. Also, springs are prone to stress cracking of the surface of the spring material which could product contaminants. In addition, the valve of this patent is assembled using press-fit machine components, a technique which creates trapped areas or dead volumes inside the unit. Dead volume areas can entrap fluids causing corrosion to occur which could ultimately effect the purity of the supply gas. Also, for ultrapure applications, such as commonly encountered in the microelectronics industry, it is highly desirable to electropolish the finishes of those surfaces which come in contact with the supply gas. It is known that springs are very difficult to electropolish and thus are more susceptible to corrosion.
Accordingly, the need exists for an improved gas isolation and containment device of simpler design and with reduced dead volume and improved surface finishes to avoid contaminants from entering the gas stream being purified and monitored. Moreover, there is a need to be able to change these devices without exposing personnel to hazardous gases and to install replacement devices without exposing the reactive material to the surrounding environment.